Are we pressing Paul's figure too far?Christianity is not a different "olive tree" from that of Judaism, but non-Jews were grafted into the same one, supported by the same "root".
If the tree is the same, why would those who were part of the Judaism tree, who entered by the flesh, be required to be born of the spirit to be in the same tree? Were they put out of the "olive tree" they were once part of and required to enter into the same tree once again by another way if the tree was the same?
If "the Church" is the same tree as Judaism, and none have ever been saved who are not in "the Church", then what of all the gentiles both before and after the Law of Moses came for the Jews, were there none saved other than Jews?
I have long believed that gentiles could be saved apart from the Law, just the same as they could before the Law came, as Noah, Abraham, et al were. The Law was for the Jews alone, addressed to those "brought out of Egypt". (this did not preclude one from becoming a Jew.) Is there any place in scripture where we are informed that all the other peoples of the earth, without exception, though they believed in the true God, were unacceptable to God at the time the Law was given?
If people could be acceptable to God, apart from the Law, prior to the coming of Messiah, then there were two Churches in existence or Israel alone did not comprise "the Church".